For vehicle electrical system topologies, conventional variants having multivoltage generators, i.e., variable-voltage generators, and downstream double-layer capacitors (DLC) or ultracapacitors (UCAP) are designed for a variable voltage level greater than 14 V, generally 30 V to 40V.
It is thus possible to increase the peak performance of the vehicle electrical system, typically for optimizing the recovery of electrical energy, i.e., the recuperation capacity. This is achieved by increasing the maximum generator power at fairly high voltage, and providing one of the mentioned capacitors as a recuperation store with increased capability for peak charge acceptance. Because an ultracapacitor has a very large number of serial cells in order to achieve the high voltage, and a DC/DC converter is designed for coupling the main vehicle electrical system to the vehicle-power supply system with variable voltage for providing a power P which is generally greater than 1.5 kW, the mentioned modules result in high costs.
In addition, there is the option of coupling high-power consumers to a vehicle power supply system of a vehicle electrical system of this type. However, this has limitations due to the greatly fluctuating voltage, which is low prior to the recuperation and is subsequently high. Likewise, conventional topology variants supply a higher voltage to high-power consumers by serial connection of an energy store (a capacitor or a second battery, for example) in series with the vehicle electrical system battery which is already present. The base vehicle electrical system of the vehicle electrical system, having a standard generator and further modules, is only slightly influenced by these changes in the vehicle power supply system.
In these topologies, an electrically insulating DC/DC converter is generally used for supplying the additional energy store. This results in the option of supplying high-power consumers with an increased voltage and with minimal effects on the rest of the vehicle electrical system caused by the voltage dip at high current load, for example. However, the additional expenditure for achieving this single function is relatively high.
A device for supplying power, in particular for a vehicle electrical system, is described in German Patent Application No. DE 10 2004 043 129 A1. An electric machine which is operable as a starter generator with the aid of a pulse width modulation inverter and a changeover switch is connected to the battery and the vehicle electrical system. This connection is broken via the changeover switch, so that a capacitor is connected to the pulse width modulation inverter. The starter generator may be operated in generator mode as well as in engine mode. In addition, recovery of electrical energy into the battery or the capacitor is possible when a deceleration is carried out in generator mode with the aid of the starter generator.